The present invention relates to a blood plasma separating apparatus, and more particularly to an apparatus for separating plasma from whole blood by a centrifugal shearing force generated by rotation.
Separation of blood elements which separates whole blood into plasma and blood cells such as red blood cells and white blood cells is conventionally conducted. Mostly centrifugal separation is employed as the method for this plasma separation, but use of membrane filtration by means of plasma separating membranes is increasing. In this membrane filtration, the filtration efficiency drops quickly because of clogging of membrane pores by blood cells, when simply flowing blood along one side of a plasma separating membrane. To prevent such blockage of the membrane filter, a plasma separation apparatus is proposed in U.S. Pat. No. 4,753,729, which has a rotor with the cylindrical side wall covered by a plasma separating membrane and a housing rotatably receiving the rotor, and flows whole blood through the space between the rotor and the housing while rotating the rotor.
A cross-sectional view of the above plasma separating apparatus is shown in FIG. 7. This plasma separating apparatus 100 has a cylindrical housing 112 and a rotor 120. The housing 112 comprises an upper end cap 114, a blood inlet port 147 disposed near the upper end of the housing 112, a blood outlet port 148 disposed at the bottom end of the housing 112, and the bottom end 116 provided with a plasma outlet port 118.
The rotor 120 is disposed in a vertical position between the upper end cap 114 and the bottom end 116 of the housing 112. The rotor 120 has a central mandrel part 122 and in the outer periphery of the mandrel 122 circumferential plasma channels 124 are formed. A plasma separating membrane 128 is attached to the outer surface of the rotor 120 so as to cover the plasma channels 124. The plasma channels 124 communicate with a central axis bore 126 through longitudinal grooves (not shown) intersecting them and a plasma channel 127. The central bore 126 communicates with the plasma outlet port 118. The rotor 120 rotates about an upper pivot pin 129 fitted at its upper end in the upper end cap 114.
In the prior art of FIG. 7, the rotary spinner 120 is mounted in the upper end cap 114 to rotate about an upper pivot pin 129 which is press fitted as its upper end in the end cap 114, the lower end of the pin being seated within a cylindrical bearing surface 130 in an end cylinder 132 attached to or forming an integral part of the rotary spinner 120. The lower end of the pin 129 protrudes into a small chamber 133 adjacent the bearing surface 130 so that the lower end of pin 129 does not dig into the end cylinder 132.
A ferromagnetic drive element 134 is mounted on a thin cylinder 132 formed in the upper end of the rotor 120, perpendicularly to the central axis of the rotor 120. The ferromagnetic drive element 134 receives a driving force through the wall of the housing 112 for indirect driving of the rotor 122. A drive motor 135 disposed outside the housing 112 drives an annular drive member 136. The drive member 136 has four permanent magnets 138 disposed at equal spaces in the inner side wall of the drive member 136. The permanent magnets 138 induce magnetic field through the ferromagnetic rotor drive element 134. When the drive member 136 rotates, the ferromagnetic drive element 134 is driven through magnetic coupling and thereby rotates the rotor 120. An enlarged scale sectional view of the bottom part of this plasma separating apparatus is shown in FIG. 8. As shown in FIG. 8, the central bore 126 formed along the central axis of the rotor 120 communicates with a central aperture 140 in a pivot pin 142 seated concentrically in the bottom end 116 of the housing 112. An O-ring seal 144 is mounted on a bearing surface 145 of the pivot pin 142.
Constructed as described above, The plasma is filtered through the membrane 128 into the plasma channels 124 with enhanced vortex action generated by the rotation of the rotor 120, collects in the plasma channel 127 through longitudinal grooves (not shown), and then flows out from the outlet port 118 through the central aperture 140 in the pivot pin 142.
In this plasma separating apparatus 100, the plasma discharge passage is disposed in the pivot mechanism as shown in FIG. 8. Therefore, the rotor 120 must be rotatably held and at the same time the plasma discharge passage must be sealed fluid-tight by means of the bottom end of the rotor 120, the pivot pin 142, and the O-ring seal 144. However, it is very difficult to hold the rotor 120 rotatably and to seal the plasma discharge passage fluid-tight at the same time. It is especially difficult to seal fluid-tight with an O-ring seal 144 alone. For this reason, there is a problem with this plasma separating apparatus 100 that blood cells flowing between the inside wall of the bottom end 116 of the housing 112 and the bottom end of the rotor 120 can mix in the separated plasma flowing in the central aperture 140 in the pivot pin 142, passing through the space around the pivot pin 142 and leaking in the aperture 140. This apparatus is thus not satisfactory to collect pure plasma.